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# ORDER BY Clause

## 1. Syntax Overview

```sql
ORDER BY sortItem (',' sortItem)*

sortItem
    : expression (ASC | DESC)? (NULLS (FIRST | LAST))?
    ;
```

### 1.1 ORDER BY Clause

- Used to sort the result set at the final stage of a query. Based on the specified sorting conditions, the rows in the query result can be arranged in ascending (ASC) or descending (DESC) order.
- Provides control over the sorting position of NULL values, allowing users to specify whether NULL values are placed at the beginning (NULLS FIRST) or the end (NULLS LAST) of the result.
- By default, `ASC NULLS LAST` is used, i.e., values are sorted in ascending order with NULL values placed last. The default sorting order can be changed by manually specifying other parameters.
- The ORDER BY clause is executed before the LIMIT or OFFSET clause.
- Since V2.0.11, the ORDER BY clause supports referencing aliases explicitly defined in the SELECT clause. When a name is directly referenced in ORDER BY, it is first resolved as a SELECT output alias; if multiple aliases with the same name exist in the SELECT list, an ambiguity error will be thrown when referencing that alias.

## 2. Sample Dataset

The [Example Data page](../Reference/Sample-Data.md) provides SQL statements to construct table schemas and insert data. By downloading and executing these statements in the IoTDB CLI, you can import the data into IoTDB. This data can be used to test and run the example SQL queries included in this documentation, allowing you to reproduce the described results.

#### Example 1: Query Data of the Past Hour Sorted by Time in Descending Order

```sql
SELECT *
  FROM table1
  WHERE time >= 2024-11-27 00:00:00  and time <= 2024-11-29 00:00:00
  ORDER BY time DESC;
```

Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                   modifytime|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-28T11:00:00.000+08:00|  上海|    3001|      100|       C|         90|       88.0|    45.1|  true|2024-11-28T11:00:12.000+08:00|
|2024-11-28T10:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2|  null|2024-11-28T10:00:11.000+08:00|
|2024-11-28T09:00:00.000+08:00|  上海|    3001|      100|       C|         90|       null|    40.9|  true|                         null|
|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    null|  null|2024-11-28T08:00:09.000+08:00|
|2024-11-27T16:44:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|2024-11-26T16:37:08.000+08:00|
|2024-11-27T16:43:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:42:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:41:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-26T16:37:04.000+08:00|
|2024-11-27T16:40:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-26T16:37:03.000+08:00|
|2024-11-27T16:39:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-27T16:38:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-26T16:37:01.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 11
It costs 0.148s
```

#### Example 2: Query Data of All Devices Sorted by device_id in Ascending Order and Time in Descending Order, with NULL temperature Displayed First

```sql
SELECT *
  FROM table1
  WHERE time >= 2024-11-27 00:00:00  and time <= 2024-11-29 00:00:00
  ORDER BY temperature NULLS FIRST, time DESC;
```

Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                   modifytime|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-28T09:00:00.000+08:00|  上海|    3001|      100|       C|         90|       null|    40.9|  true|                         null|
|2024-11-27T16:44:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|2024-11-26T16:37:08.000+08:00|
|2024-11-27T16:43:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    null| false|                         null|
|2024-11-27T16:42:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.2| false|                         null|
|2024-11-27T16:38:00.000+08:00|  北京|    1001|      101|       B|        180|       null|    35.1|  true|2024-11-26T16:37:01.000+08:00|
|2024-11-28T10:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2|  null|2024-11-28T10:00:11.000+08:00|
|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    null|  null|2024-11-28T08:00:09.000+08:00|
|2024-11-27T16:41:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-26T16:37:04.000+08:00|
|2024-11-27T16:40:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-26T16:37:03.000+08:00|
|2024-11-27T16:39:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    35.3|  null|                         null|
|2024-11-28T11:00:00.000+08:00|  上海|    3001|      100|       C|         90|       88.0|    45.1|  true|2024-11-28T11:00:12.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 11
It costs 0.060s
```

#### Example 3: Query the Top 10 Rows with the Highest Temperature

```sql
SELECT *
  FROM table1
  ORDER BY temperature DESC NULLS LAST
  LIMIT 10;
```

Results:

```sql
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|                         time|region|plant_id|device_id|model_id|maintenance|temperature|humidity|status|                   modifytime|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
|2024-11-30T09:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    35.2|  true|                         null|
|2024-11-26T13:38:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:38:25.000+08:00|
|2024-11-30T14:30:00.000+08:00|  上海|    3002|      101|       F|        360|       90.0|    34.8|  true|2024-11-30T14:30:17.000+08:00|
|2024-11-26T13:37:00.000+08:00|  北京|    1001|      100|       A|        180|       90.0|    35.1|  true|2024-11-26T13:37:34.000+08:00|
|2024-11-29T18:30:00.000+08:00|  上海|    3002|      100|       E|        180|       90.0|    35.4|  true|2024-11-29T18:30:15.000+08:00|
|2024-11-28T11:00:00.000+08:00|  上海|    3001|      100|       C|         90|       88.0|    45.1|  true|2024-11-28T11:00:12.000+08:00|
|2024-11-28T10:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    35.2|  null|2024-11-28T10:00:11.000+08:00|
|2024-11-28T08:00:00.000+08:00|  上海|    3001|      100|       C|         90|       85.0|    null|  null|2024-11-28T08:00:09.000+08:00|
|2024-11-29T10:00:00.000+08:00|  上海|    3001|      101|       D|        360|       85.0|    null|  null|2024-11-29T10:00:13.000+08:00|
|2024-11-27T16:40:00.000+08:00|  北京|    1001|      101|       B|        180|       85.0|    null|  null|2024-11-26T16:37:03.000+08:00|
+-----------------------------+------+--------+---------+--------+-----------+-----------+--------+------+-----------------------------+
Total line number = 10
It costs 0.069s
```

#### Example 4: Aggregate by Time Bucket and Sort by Alias (via SELECT Alias)

```sql
SELECT date_bin(1h, time) AS hour_time, AVG(temperature) AS avg_temperature
  FROM table1
  WHERE time >= 2024-11-27 00:00:00  and time <= 2024-11-30 00:00:00
  GROUP BY hour_time
  ORDER BY hour_time;
```

Results:

```sql
+-----------------------------+---------------+
|                    hour_time|avg_temperature|
+-----------------------------+---------------+
|2024-11-27T16:00:00.000+08:00|           85.0|
|2024-11-28T08:00:00.000+08:00|           85.0|
|2024-11-28T09:00:00.000+08:00|           null|
|2024-11-28T10:00:00.000+08:00|           85.0|
|2024-11-28T11:00:00.000+08:00|           88.0|
|2024-11-29T10:00:00.000+08:00|           85.0|
|2024-11-29T11:00:00.000+08:00|           null|
|2024-11-29T18:00:00.000+08:00|           90.0|
+-----------------------------+---------------+
Total line number = 8
It costs 0.079s
```